Reference is made to U.S. Pat. No. 3,789,738 in the name of R. F. Horner and U.S. Pat. application Ser. No. 578,693 filed May 19, 1975 in the name of W. G. Price, both of which are assigned to the assignee of the present application, for two examples of prior art disclosing different ways of extending the travel of a brake actuating piston. It will be noted that Pat. No. 3,789,738 teaches a collapsible piston whereas Pat. application Ser. No. 578,693 teaches a piston slidably carried in a fluid pressure actuated cylinder which is advanced in the direction of movement of the piston.
The present invention is an improvement over the above identified prior art devices in that it provides a force balanced fluid pressure responsive cylinder which is actuated by a fluid pressure responsive piston slidably contained therein to extend the piston travel without amplifying the brake actuating force provided by the piston regardless of the fluid pressure acting against the piston and wherein the volumetric requirement of pressurized fluid for a given travel of the piston is constant during actuation of the cylinder.